Manufacture of pyranthrones

ABSTRACT

A new process for the manufacture of pyranthrones (I) from 2,2&#39;&#39; -dialkyl-1,1&#39;&#39;-dianthraquinonyls (II) by heating (II) at from 150* to 210* C. in polar organic solvents in the presence of alkali metal acetates.

mite States Patent Rock [451 June 27, 1972 MANUFACTURE OF PYRANTHRONESAppl. No.: 79,681

Foreign Application Priority Data Oct. 14, 1969 US. Cl... ..260/360 Int.Cl. Field of Search ..260/ 3 6O Germany ..P 19 51 7089' References CitedOTHER PUBLICATIONS Lubs, The Chemistry of Synthetic Dyes and Pigments,pp. 450-45l,(l955) Primary Examiner-Lorraine A. Weinberger AssistantExaminer-E. Jane Skelly Attorneylohnston, Root, OKeeffe, Keil, Thompson& Shurtleff ABSTRACT A new process for the manufacture of pyranthrones(I) from 2,2-dialkyl-l ,1-dianthraquinonyls (II) by heating (II) at from150 to 210 C. in polar organic solvents in the presence of alkali metalacetates.

6 Claims, No Drawings MANUFACTURE OF PYRANTHRONES The present inventionrelates to a new process for the manufacture of pyranthrones from2,2'-dialkyl-1,l-dianthraquinonyls.

German Patent No. 175,067 discloses that pyranthrones may be obtained byheating 2,2-dimethyl-1,1-dianthraquinonyls in alkali metal hydroxidemelts, in the presence or absence of alcohols, at temperatures of from140 to 250 C.

This prior art process suffers from the disadvantage that such alkalimetal hydroxide melts are difficult to handle and the products of theprocess always contain impurities which greatly restrict their use asdyes, especially as pigment dyes. Since this drawback may only beobviated by complicated and consequently uneconomical purifyingprocesses, an object of this invention is to provide a process whichenables pyranthrones to be manufactured in a simple manner and in therequired high degree of purity.

This and other objects are achieved in accordance with this invention bya process in which pyranthrones are manufactured by heating2,2'-dialkyll,l'-dianthraquinonyls in polar organic solvents and in thepresence of alkali metal acetates at temperatures of from 150 to 210 C.

Particularly suitable starting materials for the new process are2,2-dialkyl-l ,1 -dianthraquinonyls having Formula II:

from which pyranthrones having Formula I are formed. In the Formula Iand 11 R stands for hydrogen or an alkyl having one to two carbon atomsand X and Y each stands for hydrogen, halogen such as chlorine orbromine, or an alkyl having one to two carbon atoms.

The manufacture of unsubstituted pyranthrones is of particularindustrial interest.

Neither the amount of alkalimetal acetate used nor the amount of saidsolvents used is critical for the success of the reaction. The presenceof catalytic amounts of alkali acetate, for example, is sufficient tocause cyclization. However, in order to keep the reaction time to aminimum, it is particularly advantageous to use from 0.5 to 1 mole ofalkali metal acetate per mole of compound having Formula II.Particularly suitable alkali metal acetates are sodium the alkali metalacetates is carried out in polar organic solvents which are stable underthe reaction conditions. Examples of such solvents are alcohols such asethylene glycol, diethylene glycol or dipropylene glycol or organicsolvents containing the group such-as N,N-dialkylcarboxylamides, e.g.N,N-dimethyl acetamide, N,N-dimethyl formamide or compounds, such as N-methylpyrrolidone, in which the group forms part of a heterocyclic ring.

There are no restrictions as regards the type and quantity of solvent tobe used, for example when low-boiling solvents are used, the process maybe carried out under pressure. However, it is advantageous to usesolvents of the said type which boil within or above the specifiedtemperature range. N-

methylpyrrolidone or dipropylene glycol and ethylene glycol have provedto be particularly advantageous. The amount of solvent used depends ontechnical conditions under which the reaction mixture can still bestirred. Where conventional reac- 5 tion vessels are used, it isadvantageous to use an amount of solvent which is equal to from two tofour times the weight of dianthraquinonyl used.

The reaction to form the pyranthrones is complete after about one to twohours. The products of the process may be isolated in a simple manner,for example by suction filtration, washing and drying.

The pyranthrones produced by the new process are distinguished by such ahigh degree of purity that they can be used as dyes without thenecessity for further purification.

The invention is further illustrated by the following examples in whichparts are by weight.

EXAMPLE 1 30 parts of 2,2'-dimethyl-l,l-dianthraquinony1 is heated with4 parts of anhydrous sodium acetate in 60 parts of N- methylpyrrolidoneat from 180 to 190 C. for 1 1/2 hours. The mixture is then cooled toroom temperature and the precipitated pyranthrone is isolated by suctionfiltration and washed with water until it is free from sodium acetate.After drying, there are obtained parts of pyranthrone in the form ofcoarse orange-brown crystals.

If the dry 2,2-dimethyl-1,l-dianthraquinonyl is replaced by theequivalent amount of a filter cake of this compound moist with water andthe water is distilled off from the reaction mixture until the reactiontemperature is reached, pyranthrone is obtained in the same yield andpurity.

EXAMPLE 2 20 parts of 2,2-dimethyl-4,4-dichloro-1,1-dianthraquinonyl isheated in 50 parts of ethylene glycol containing 5 parts of potassiumacetate at 170 C. for 1 hour. The reaction mixture is then cooled toroom temperature and suction filtered. The solid residue is washed withuntil it is free from potassium acetate and dried. There are thusobtained 16 parts of 1,9- dichloropyranthrone in the form of orangecrystals.

I claim:

1. A process for the manufacture of pyranthrones having the formula:

are heated in polar organic solvents and in the presence of alkali metalacetates at temperatures of from 150 to 210 C.

2. A process as claimed in claim 1 wherein compounds having formula llwhere X and Y stand for chlorine or bromine are reacted.

3. A process as claimed in claim 1 wherein the alkali metal acetate usedis sodium or potassium acetate.

4. A process is claimed in claim 1 wherein from 0.5 to 1 mole of alkalimetal acetate is used per mole of 2,2-dia.lkyll,l-dianthraquinonyl (II).

5. A process as claimed in claim 1 wherein the polar organic solventsused are selected from the group consisting of polyols, polyglycols, andsolvents which contain the group

2. A process as claimed in claim 1 wherein compounds having formula IIwhere X and Y stand for chlorine or bromine are reacted.
 3. A process asclaimed in claim 1 wherein the alkali metal acetate used is sodium orpotassium acetate.
 4. A process is claimed in claim 1 wherein from 0.5to 1 mole of alkali metal acetate is used per mole of2,2''-dialkyl-1,1''-dianthraquinonyl (II).
 5. A process as claimed inclaim 1 wherein the polar organic solvents used are selected from thegroup consisting of polyols, polyglycols, and solvents which contain thegroup and which the group may form part of a heterocyclic ring.
 6. Aprocess as claimed in claim 1 wherein the polar organic solvents usedare selected from the group consisting of ethylene glycol, diethyleneglycol, dipropylene glycol, N,N-dimethyl acetamide, N,N-dimethylformamide, N-methylpyrrolidone and mixtures thereof.